Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

Normal cooling

None of these

2. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

3. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.4

0.6

4. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

10°C

15°C

5. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

6. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

7. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

8. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

9. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

10. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

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11. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Above critical temperature

Near critical temperature of refrigerant

12. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

One heat exchanger

Four heat exchangers

13. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Equal to unity

Any one of the above

Always more than unity

14. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

15. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

16. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Carnot

Reversed Rankine

17. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

18. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

9: 1

1: 3

19. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

20. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

All of these

Room air conditioners

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21. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

22. The domestic refrigerator uses following type of compressor

Centrifugal

Axial

Miniature sealed unit

Piston type reciprocating

23. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Wet bulb temperature of air

Ambient air temperature

Dew point temperature of air

24. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Condenser and receiver

Evaporator and compressor

Compressor and condenser

25. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

Condenser tubes

26. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

27. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Brine

Ammonia

28. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Involves no change in volume

Takes place at constant entropy

Takes place at constant temperature

29. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

30. Rating of a domestic refrigerator is of the order of

0.1 ton

40 tons

10 tons

5 tons

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31. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

32. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

4.33

1.33

33. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

34. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Zero

Negative

35. For obtaining high COP, the pressure range of compressor should be

Any value

Low

High

Optimum

36. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

30 bar

15 bar

37. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

38. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

39. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

40. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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